Atmospheric Chemistry of (CF₃)₂CF–C≡N: A Replacement Compound for the Most Potent Industrial Greenhouse Gas, SF₆

Abstract

FTIR/smog chamber experiments and ab initio quantum calculations were performed to investigate the atmospheric chemistry of (CF₃)₂CFCN, a proposed replacement compound for the industrially important sulfur hexafluoride, SF₆. The present study determined k(Cl + (CF₃)₂CFCN) = (2.33 ± 0.87) × 10^-17, k(OH + (CF₃)₂CFCN) = (1.45 ± 0.25) × 10^-15, and k(O₃ + (CF₃)₂CFCN) ≤ 6 × 10^-24 cm³ molecule^-1 s^-1, respectively, in 700 Torr of N₂ or air diluent at 296 ± 2 K. The main atmospheric sink for (CF₃)₂CFCN was determined to be reaction with OH radicals. Quantum chemistry calculations, supported by experimental evidence, shows that the (CF₃)₂CFCN + OH reaction proceeds via OH addition to -C(≡N), followed by O₂ addition to -C(OH)═N·, internal H-shift, and OH regeneration. The sole atmospheric degradation products of (CF₃)₂CFCN appear to be NO, COF₂, and CF₃C(O)F. The atmospheric lifetime of (CF₃)₂CFCN is approximately 22 years. The integrated cross section (650-1500 cm^-1) for (CF₃)₂CFCN is (2.22 ± 0.11) × 10^-16 cm² molecule^-1 cm^-1 which results in a radiative efficiency of 0.217 W m^-2 ppb^-1. The 100-year Global Warming Potential (GWP) for (CF₃)₂CFCN was calculated as 1490, a factor of 15 less than that of SF₆.